I'd just make this caution: just because you experience fear and anxiety in large public gatherings does NOT make you an introvert. An introvert ENJOYS being alone, and NEEDS alone time to "recharge". They are difficult to engage not because they dread going out but because they're perfectly content where they are. It *is* possible to be a socially-awkward extrovert. Or, worse, someone who is uncomfortable with themselves in general. This type of person will (generally) cling to other people for approval/recognition, but simultaneously dread groups of people because they don't GET that approval/recognition they desire from large groups, only from small groups or individuals. People with this difficulty will often also cling to whoever they already happen to know rather than seek out new friends they have more in common with.
If you find that you dislike being alone because you aren't happy with your own company and dislike large groups because you feel awkward/not-in-control, then working on fixing your self-disapproval is more important than trying to find strategies that make you comfortable with large groups. Once you are more comfortable with yourself, you will more easily be able to deal with other people.